Many types of hoisting devices such as straddle hoists, movable cranes and cranes having movable trolleys mounted thereon, hoist loads by winding cable onto a power drum and lower the loads by unwinding the cable from the power drum. Such devices are subject to the problem of the load swaying when it is moved horizontally while supported by the hoisting device.
In prior apparatus efforts have been made to reduce the sway of loads suspended from the hoisting during hoisting movement. Such efforts have included increasing the distance between the trolley sheaves with respect to the lifting frame sheaves so that the hoisting cables diverge upwardly and thus tend to resist sway (George W. Cooper Patent No. 3,825,128 and A. J. De Stasi U.S. Pat. No. 3,086,661). Also, many patents suggest the use of a separate stablilzing system (see Hans Tax et al U.S. Pat. No. 3,746,182). Others have suggested the use of tag lines (G. H. Crittenden U.S. Pat. No. 3,532,324). Also, these patents result in additional equipment, some of which can increase the sway problems by exerting too much of a return force on the swaying load. Others have involved extensive cable and braking systems.